The present invention relates to an upper cover structure for a line printer. More specifically, the invention relates to a type thereof capable of providing pivotal movement with respect to a console frame of the line printer.
A line printer is generally provided with cover members for housing printing mechanisms. Particularly, an upper cover adapted to cover an upper printing mechanism has a structure capable of being opened or closed with a simple mannual operation in order to exchange the printing paper and/or the ink ribbon. This upper cover which covers the upper printing mechanism serves to prevent danger to the operator and to block noise generated by the printing mechanism and further to provide an electrostatic shielding function as well as to enhance the outer appearance of the printer.
FIG. 1 shows a conventional upper cover structure in which an upper cover hood 1 covers a printing mechanism 2 mounted on a box shaped console frame 4 through shock absorbing members 3. The upper cover hood 1 has a rear bottom end connected to a hinge 5 secured to the console frame 4 by a screw 6 so that the upper cover hood 1 is pivotally movable relative to the console frame 4. The upper cover hood 1 is opened by pivotal movement thereof about the hinge 5 in the clockwise direction in the drawing for exchanging the printing paper or ink ribbon (not shown) or for maintenance of a front side A of the printer.
As is well known, the upper cover hood 1 is relatively heavy, for example the cover has a weight of 7 to 8 kg for small printers and 20 to 30 kg for a large printer. Therefore, a power assisting device or balance mechanism is generally provided in order to allow easy opening or closing of the upper cover hood 1. A spring device, pneumatic or hydraulic cylinder devices and electrical power movers have been used for this purpose. In a conventional upper cover as shown in FIG. 1, at least one balance mechanism 26 utilizing a spring biasing force is employed. In the balance mechanism 26, a balance mechanism guide 12 is secured to an inner surface of a side wall of the cover hood 1 by welding or screws with a shaft 10 slidingly extending through a bore 16 formed in the guide 12. The shaft 10 has a bottom end pivotably secured to a balance mechanism holder 14 by means of a pin 17 with the balance holder 14 secured to the console frame 4 by a screw 15. The shaft 10 has an upper portion provided with a stopper pin 11a whose lower surface is in contact with a stop washer 11b disposed around the shaft 10.
Further, a lower spring 13a is disposed around the shaft 10 and is interposed between a lower surface 12a of the guide 12 and a lower stepped portion of the shaft 10 so as to normally urge the upper cover hood 1 upwardly. On the other hand, an upper spring 13b is disposed around the shaft 10 and is interposed between the stop washer 11b and an upper surface 12b of the guide 12. The biasing force of the lower spring 13a is slightly smaller than total weight of the upper cover hood 1 so that, during closure of the upper cover, immediate descent of the cover is prevented. The upper spring 13b is adapted to stop the cover at a predetermined pivotal locus and to provide a shock absorbing function upon the upper cover hood 1 being opened to the maximum. Moreover, during the opening of the cover hood 1, the biasing force of the spring 13a becomes greater than that of the spring 13b so that the upper cover hood 1 can be opened with only a small manual force. As shown, the front bottom end of the upper cover hood 1 is attached to a packing 9 which provides a sealing function on the cover as well as absorbing accidental shock due to quick closure of the cover hood 1.
The line printer generally must be maintained and maintenance is carried out at the rear portion B. Therefore, a window 18 is provided at the rear wall of the upper cover hood 1. Normally, the window 18 is closed by a window cover 7 secured to the rear wall by screws 8. To maintain the rear portion of the printer, the window cover 7 is detached from the rear wall to visually observe the rear portion or to allow the inspector to extend his hands or head through the window 18. However, with this construction, the maintenance field is restricted and little light can reach the interior of the printer thereby making the maintenance quite difficult.
The upper cover may be opened by pivotally moving it in the clockwise direction in FIG. 1 in order to let more light in. However, such opening of the cover may degrade maintenance efficiency since the distance between the window 18 and the rear printing mechanism portion is lengthened so that the inspector or operator must extend the upper part of his body through the window 18.
In order to obviate these drawbacks, it has been proposed to detach the upper cover hood 1 from the console frame 4 by releasing the screws 6 and 15. However, even if these screws can be readily removed, it is difficult as a practical matter to remove the cover hood 1 by a single operator since the cover hood 1 tends to be heavy as described above.